This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-181920, filed Jun. 28, 1999; and No. 2000-118936, filed Apr. 20, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to an ink jet recording method for carrying out dot recording at a pitch smaller than that between ink ejection openings of an ink jet recording head.
An ink jet recording head comprises a plurality of ink jet chambers each having an ink ejection opening that ejects an ink, a common ink chamber for feeding the ink into each of the ink chambers, and an ejection energy generator for causing the ink in the ink chamber to be ejected through the ink ejection opening. Known ejection energy generators include a piezoelectric member that varies the volume of the ink chamber to eject the ink through the ink ejection opening and an electrothermal conversion element that instantaneously partly evaporates the ink in the ink chamber to generate bubbles in order to vary the volume of the ink chamber, thereby ejecting the ink through the ink ejection opening. The ink ejected through the ink ejection opening is deposited on, absorbed by, and fixed to a recording medium such as paper or a film, as dots.
To increase the recording speed of such an ink jet recording head, the head is desirably elongated in a line direction correspondently to the width of the recording media, with a large number of ink ejection openings arranged at a small pitch. If, however, a large number of ejection openings are arranged at a small pitch, forming all the ink ejection openings so as to have the same pitch, the same height, and the same diameter requires a relatively high accuracy and is thus difficult to achieve. If this is feasible, the ink jet recording head will be very expensive and impractical. In addition, the ink ejection openings are likely to be blocked to degrade recorded images.
Thus, the pitch between the ink ejection openings is increased, and the first dot recording on recording media is carried out at this pitch between the ink ejection openings. Then, for the second dot recording, the recording head is moved, for example, in the line direction a distance corresponding to half of the pitch between the ink ejection openings so that each ink ejection opening is located midway between the last positions of the ink ejection openings, thereby enabling high-resolution images to be recorded at the pitch half that of the ink ejection openings. Higher-resolution images can be recorded by moving the recording head a distance corresponding to one third or one fourth of the ink ejection opening pitch. In this case, however, recording is repeated on the same recording medium three or four times, thereby reducing printing speed.
If, however, high-resolution images are recorded by shifting the dot recording on the same recording medium in the line direction, there will be a difference in density arising from a difference in time between the first printing and subsequent printings, resulting in a stripe pattern on the recording medium in a direction orthogonal with the line direction to degrade image quality.
It is an object of the present invention to provide an ink jet printing apparatus and method for recording images by shifting a head position in a line direction with respect to a recording medium while repeating dot recording a plurality of times, wherein printing is carried out a plurality of times using a print interval time determined by referencing an ink absorbing speed of recording media, to prevent occurrence of a stripe pattern caused by a difference in time associated with repeated printing, thereby enabling high-quality image recording.
Present invention provides an image printing apparatus comprises storage means for storing an absorbing speed information in a storage area, the absorption speed information is a measured speed at which a recording medium used for a printing process absorbs an ink used for the printing process; and control means for controlling an ink head so as to perform first dot recording which records a plurality of dots on the recording medium by a pitch of an ink ejection opening of the ink head, and for moving the recording medium relatively with the ink head and controlling the ink head so as to perform second dot recording which records a plurality of dots between a plurality of dots recorded by first dot recording, in accordance with a print interval time determined based on the absorption speed information stored in the storage means.
The present invention is based on new experiments with jet printers and data obtained therefrom; it is also based on the discovery and confirmation of a reproducible correlationship between a print interval time margin for preventing occurrence of a stripe pattern caused by a difference in printing time during dot printing carried out in a plurality of operations and the nature of recording media (paper) used for this printing (specifically, the speed at which the inks used are absorbed by the paper used).
Before present invention, the inventor thought, in the printing carried out by the jet printer in a plurality of operations, the possibility of a stripe pattern occurring decreases with increasing difference in printing time between the first printing and subsequent printing. Setting an extremely short print interval time, however, reduces design margins to cause unstable operations. Accordingly, the print interval time for the plurality of printing operations must be relatively long so that no stripe pattern will occur.
Then, based on analysis of an enormous amount of experiments and resulting information, the inventor has discovered a positive reproducible relationship between the speed at which the inks used are absorbed by the recording paper used and the print interval time appropriate for avoiding the occurrence of a stripe pattern. That is, a margin for the occurrence of a stripe pattern increases consistently with the ink absorption speed. And, the margin increases inversely with the printing interval time. The relationship between the (ink absorbing time of the paper) and the (print interval time) is specific, stable, and reproducible enough to be expressed by an inequality using fixed constants.
If printing is carried out in a plurality of operations by using this relationship to set an optimal print interval time for recording paper to be used, the largest margin is obtained while preventing the occurrence of a stripe pattern. Thus, the present invention can provide an image printing apparatus and method that can prevent the occurrence of a stripe pattern while stabilizing printing operations.
The relationship between the (ink absorption speed of the paper) and the (print interval time) can be expressed using specific values. Accordingly, by determining the (print interval time) based on these values to perform a plurality of printing operations, a more reliable image printing apparatus and method can be implemented.
Furthermore, since the ink absorbing speed has a relationship with the temperature of the ink, a more sophisticated and stable image printing apparatus and method can be realized by measuring the current ink temperature in the image printing apparatus and determining the print interval time taking a result of the measurement into consideration.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combination particularly pointed out hereinafter.